Bump minimum mautrix-python version so docker picks it up

requirements.txt

@@ -4,5 +4,5 @@ alembic>=1,<2
 ruamel.yaml>=0.15.94,<0.17
 commonmark>=0.8,<0.10
 python-magic>=0.4,<0.5
-mautrix>=0.5.3,<0.6
+mautrix>=0.5.4,<0.6
 fbchat-asyncio>=0.6.1,<0.7